This invention relates to a fluid displacement apparatus and, more particularly, to an axial clearance adjustment mechanism for a scroll-type fluid displacement apparatus.
Scroll-type fluid displacement apparatus are well-known in the prior art. For example, U.S. Pat. No. 801,182 (Cruex) discloses a device including two scroll members each having a circular end plate and a spiroidal or involute spiral element. These scroll members are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of sealed off fluid pockets. The relative orbital motion of the scroll members shifts the line contacts along the spiral curved surfaces and, therefore, the fluid pockets change in volume. Since the volume of the fluid pockets increases or decreases, depending on the direction of the oribital motion, the scroll-type fluid displacement apparatus is applicable to compress, expand or pump fluids.
In comparison with conventional compressors of the piston type, the scroll-type compressor has certain advantages, such as fewer parts and continuous compression of fluid. However, one of the problems encountered in prior art scoll-type compressors is ineffective sealing of the fluid pockets. Axial and radial sealing of the fluid pockets must be maintained in a scroll-type compressor in order to achieve efficient operation. The fluid pockets in a scroll-type compressor are defined by both line contacts between the interfitting spiral elements and the axial contacts between the axial end surfaces of the spiral elements and the inner surfaces of the adjacent end plates. Thus, the clearance between the scroll members, particularly the axial clearance between the axial end surfaces of the spiral elements and the inner surfaces of the end plates of the scroll members, exerts an influence upon the volumetric efficiency or energy efficiency of the scroll-type compressor.
Generally, the fixed scroll member of a prior art scroll-type fluid apparatus is fixedly disposed within the housing. In some cases, axial clearance between the axial end surface of the spiral element of one scroll member and the inner surface of the end plate of the other scroll member is adjusted by placing a plurality of shims between the casing and the end plate of the fixed scroll member. However, since there is a limit to the thickness of the shims, very fine adjustment of axial clearance is difficult to achieve. In the event the axial clearance is too great, the gap between the axial end surface of the spiral element of one scroll member and the inner surface of the end plate of the other scroll member is sealed by a sealing element placed between these surfaces.
Furthermore, in the above prior art scroll-type apparatus, one of the scroll members generally is formed of hard material and the other scroll member is formed of slightly softer material in order to reduce weight. This difference in hardness results in increased wear of the end plate of the softer scroll member due to constant sliding contact by the axial sealing element placed between this end plate and the spiral element of the hard scroll member. Therefore, the inner surface of the end plate of the softer scroll member normally must be provided with a bottom plate for preventing wear of the end plate.
One solution to the above problem is described in commonly assigned, Terauchi U.S. Pat. No. 4,460,321 issued on July 17, 1984. The apparatus disclosed in that patent has an annular opening which is formed through the center portion of the end plate of the cup-shaped casing of the apparatus, the opening having a threaded portion at the inner surface thereof. An adjusting screw is screwed into the threaded portion, the inner end of the adjusting screw fitting against the end surface of the end plate of the fixed scroll member to push it toward the orbiting scroll, thereby setting suitable axial clearance between the scroll members. However, since during assembly of the apparatus the fixed scroll is initially supported within the cup-shaped casing only by contact between the peripheral surface of the end plate and the adjacent inner surface of the cup-shaped casing, if the adjusting screw is moved the fixed scroll member often is skewed relative to the orbiting scroll. Thus, during adjustment of axial clearance, parallelism of the scroll end plates cannot be maintained, and effective axial sealing is lost.